Thermoplastic compositions, process for preparing them and their application in the production of industrial articles

ABSTRACT

The compositions contain a) less than 90% and at least 2% by weight of at least one ethylene polymer (A), and optionally, at least one α-olefin having from 3 to 12 carbon atoms, said polymer containing at least 70% in moles of patterns derived from ethylene, and b) more than 10% and up to 98% by weight of at least one polymer (B) containing at least 85% in moles of patterns derived from at least one α-olefin having from 3 to 12 carbon atoms and at the most 15% in moles of patterns derived from ethylene, and are characterized in that the polymer (A) is a modified polymer of which the measured limit viscosity is comprised between 1.3 and 100 times its limit viscosity calculated from the distribution of molecular masses. The compositions are obtained by a process consisting in providing a polymer of ethylene and, optionally, of at least one α-olefin having from 3 to 12 carbon atoms in the presence, on the one hand, of at least one initiator of free radicals in a quantity comprised between 0,001 and 0.3 parts by weight of the initiator for one hundred parts by weight of said polymer at a temperature higher than the melting temperature of said polymer during a time at least equal to one tenth of the half life time of the initiator at the temperature considered, and, on the other hand, of at least one polymer (B). Application to the production of industrial articles by extrusion-blowing of sheaths or hollow bodies, extrusion of films by means of flat dies, roto-moulding, injection or coating.

Compositions consisting of ethylene polymers and polypropylene arealready known.

Thus, document FR-A-2,529,563 describes compositions comprising from 10to 40% by weight of isotactic polypropylene and from 60 to 90% by weightof at least one copolymer of ethylene and α-olefins containing at least4 carbon atoms, with a relative density of between 0.905 and 0.940 and amelt index of between 0.2 and 3 dg/min, the content of α-olefin units inthe copolymer being between 1 and 8 mol %. These compositions permit themanufacture of monooriented filaments exhibiting, in particular, a hightenacity.

Furthermore, document EP-A-0,052,557 describes compositions which havean improved impact strength and which contain from 40 to 98% by weightof isotactic polypropylene and from 2 to 60% by weight of a copolymerwith a relative density not exceeding 0.935, obtained from 85 to 96% byweight of ethylene and from 4 to 15% by weight of at least one α-olefin.

Document FR-A-2,519,007 (U.S. Pat. No. 4,486,579) also disclosesmodified copolymers of ethylene and of at least one α-olefin containingfrom 3 to 12 carbon atoms, containing from 0.5 to 10 mol % of unitsderived from the said α-olefin, which are characterized in that theirmeasured limiting viscosity is between 1.5 and 10 times their limitingviscosity calculated from the molecular mass distribution.

A way has now been found of obtaining thermoplastic compositionsexhibiting improved mechanical properties, in particular low-temperatureresilience, elongation at break and tensile strength, when compared withthe known compositions, by using in combination with the polypropylene,instead of a copolymer of ethylene and α-olefins, a polyethylene or anethylene/α-olefin co-polymer prepared by Ziegler catalysis and subjectedto a modification such that the ratio of its measured and calculatedlimiting viscosities lies within a certain range.

The subject of the present invention is a thermoplastic compositioncontaining:

a) less than 90% and at least 2% by weight of at least one polymer (A)of ethylene and, where appropriate, of at least one α-olefin containingfrom 3 to 12 carbon atoms, the said polymer containing at least 70 mol %of units derived from ethylene, and

b) more than 10% and up to 98% by weight of at least one polymer (B)containing at least 85 mol % of units derived from at least one α-olefincontaining from 3 to 12 carbon atoms and not more than 15 mol % of unitsderived from ethylene, which composition is characterized in that thepolymer (A) is a modified polymer whose measured limiting viscosity isbetween 1.3 and 100 times its limiting viscosity calculated from themolecular mass distribution.

Polymer (A) is intended to mean a polymer obtained by homopolymerizationof ethylene or by copolymerization of ethylene with at least oneα-olefin containing from 3 to 12 carbon atoms in the presence of aZiegler-type catalyst system comprising, for example, at least onecatalyst based on a transition metal of groups IVB to VIB of thePeriodic Classification and, where appropriate, at least one activatorcomprising a hydride and/or an organometallic derivative of a metal ofgroups IA to IIIA of the Periodic Classification, and modified, forexample, by the action of a small quantity of at least one free radicalinitiator, so that its measured limiting viscosity lies between 1.3 and100 times its limiting viscosity calculated from the molecular massdistribution. These concepts of modification and of limiting viscositiesare described in detail in the document FR-A-2,519,007. The modificationof the ethylene homopolymer or copolymer may also be carried out bydispersing the free radical initiator, before it acts upon the saidhomopolymer or copolymer, in a polymeric phase comprising at least onepolymer containing at least 90 mol % of units derived from at least oneα-olefin containing from 3 to 12 carbon atoms and not more than 10 mol %of units derived from ethylene, the said phase being present in suchquantity that its proportion in the resulting composition is between 0.2and 10% by weight.

The polymer (A) generally has a relative density (determined accordingto ASTM standard 1505) of between 0.86 and 0.97. Depending on theintended application, a polymer which is predominantly rathercrystalline or predominantly rather amorphous will be chosen.

The polymer (A) generally has a standard melt index (measured accordingto ASTM standard D 1238 - condition E) chosen between 0.05 and 150dg/min, advantageously between 10 and 30 dg/min when the compositionsare intended to be converted by injection moulding, advantageouslybetween 0.2 and 2 dg/min when the compositions are intended to beconverted into films, particularly by blow-extrusion of tubular bubbles.

The α-olefin forming part of the constitution of the copolymers (A) isadvantageously chosen from propylene, 1-butene, 1-pentene, 1-hexene,4-methyl-1-pentene, 1-octene and mixtures thereof.

The polymer (B) may be, in particular, polypropylene (particularlyisotactic polypropylene), poly-1-butene, poly(4-methyl-1-pentene), apoly(propylene-ethylene) or a poly(1-butene-ethylene) containing atleast 85 mol % of units derived from propylene or 1-butene respectively,a poly(propylene/1-butene/ethylene) containing less than 15 mol % ofunits derived from ethylene, or a poly(propylene-1-butene). The polymer(B) advantageously has a melt index (according to ASTM standard D 1238at 230° C. under a 5 kg load) of between 0.2 and 150 dg/min.

Another subject of the present invention is a process for preparing acomposition such as described above, characterized in that it consistsin bringing a polymer of ethylene and, where appropriate, of at leastone α-olefin containing from 3 to 12 carbon atoms, into contact with

on the one hand, at least one free radical initiator, in a quantity ofbetween 0.001 and 0.3 parts by weight of initiator per 100 parts byweight of the said polymer at a temperature above the meltingtemperature of the said polymer, for a period greater than or equal toone tenth of the half-life of the initiator at the temperature inquestion, and

on the other hand, at least one polymer (B).

Bringing the said polymer into contact with the free radical initiatorenables a modified polymer (A) to be obtained.

According to a first alternative form of the process according to theinvention, the polymer (B) is added to the modified polymer (A) afterthe latter has been obtained. This operating procedure means that themodified polymer (A) is prepared in a first step, for example accordingto a technique such as that described in document FR-A-2,519,007 andthen the polymer (B) is added to it in a second step. This addition maytake place in a mixer or a machine for converting plastics such as anextruder. Advantageously, each of the polymers (A) and (B) is reduced toa finely divided state, for example into the form of granules which arethen blended dry and which thus provide a composition which is ready foruse. It is also possible to compound the mixture of the polymers (A) and(B) and to extrude it hot, and to convert the composition directly intofinished objects, or to granulate it.

According to another alternative form of the process according to theinvention, the free radical initiator is dispersed in at least onefraction of the polymer (B) at a temperature below the decompositiontemperature of the said initiator, before it is brought into contactwith the polymer of ethylene and, where appropriate, of α-olefin, to bemodified. The dispersion of the initiator in at least one fraction ofthe polymer (B) is produced by any known means, chosen as a function ofthe physical state of the constituents and/or of the device chosen forbringing the dispersion of the initiator into contact with the polymerto be modified. If the polymer (B) needs to be heated, the operation isadvantageously carried out by compounding at such a temperature that thefree radical initiator does not decompose or is only slightly affected.The dispersion obtained is then brought into contact with the polymer tobe modified and, where appropriate, with a complementary quantity ofpolymer (B) so as to obtain the desired composition, advantageously in amachine for converting polymers, such as a kneader or a single-screw ortwin-screw extruder. This bringing into contact may be carried outaccording to a noncontinuous process; the polymer to be modified, whichis in the form of powder of particle size preferably between 1 and 500μm or of granules is then introduced into the conversion machinesimultaneously with the initiator dispersion and, where appropriate, thecomplementary quantity of polymer (B). The initiator dispersion may alsobe homogenized beforehand with the polymer to be modified and, whereappropriate, with the complementary quantity of polymer (B), for exampleby powder or granulate blending, the homogeneous mixture being thenintroduced into the conversion machine. This bringing into contact mayalso be carried out continuously and directly in a unit formanufacturing the (co)polymer to be modified.

According to a third alternative form of the process according to theinvention, the polymer to be modified is mixed with at least onefraction of the polymer (B) before it is brought into contact with thefree radical initiator. This operation may be carried out, for example,by combining extruders in series.

According to a fourth alternative form, the bringing of the free radicalinitiator into contact with the polymer to be modified takes placesimultaneously with the bringing into contact with the polymer (B), forexample by dry blending. The blend obtained is then extruded at theusual temperature and for a usual time in order to produce thecomposition according to the invention.

Among the free radical initiators which are suitable for implementingthe process according to the invention there may be mentioned, inparticular:

peroxygen compounds such as, for example, peroxides, peresters andhydroperoxides,

diazo compounds such as an 2,2'-azobis(acyloxyalkane) like2,2'-azobis(acetoxypropane) and 2,2'-azobis(2-acetoxy-4-methylpentane),or such as 1,1'-azobis(1-formyloxycyclohexane), and

hydrocarbons containing labile carbon-carbon bonds such as, for example,diaryldialkylalkanes, like 2,3-diphenyl-2,3-dimethylbutane (commonlyreferred to by the name biscumyl) or 3,4-diphenyl-3,4-dimethylhexane.

The quantity of initiator to be employed depends on the degree ofmodification which it is intended to impart to the polymer to bemodified. For a given degree of modification it varies proportionatelyto the molecular mass of the initiator.

According to their melt index, the compositions according to theinvention may be converted into industrial articles by techniques whichare as diverse as:

in the case of a standard melt index (MI) of approximately between 0.1and 3: blow-extrusion of bubbles or of hollow bodies and film extrusionusing a flat die,

in the case of a standard melt index of approximately 2 and 10:rotational moulding and injection blow-moulding of hollow bodies,

in the case of a standard melt index of approximately between 10 and100: injection moulding and coating.

The following nonlimiting examples are intended to illustrate theinvention.

I. Polymers employed.

The polymers to be modified (P) which were employed were the productsdescribed in Table I below with the indication of their molar content C₂of units derived from ethylene (expressed in percent), their relativedensity d (according to ASTM standard D 1505) and their melt index MI(measured according to ASTM standard D 1238 at 190° C. under 2.16 kg,and expressed in dg/min). These polymers (P) are marketed by CdF ChimieEthylene et Plastiques under the names which also appear in Table I. Thepolymers P1 to P3 are copolymers of ethylene and of 1-butene. Thepolymers P4, P5 and P6 are terpolymers of ethylene, propylene and1-butene.

The polymer (B) employed was either a propylene homopolymer marketedunder the name Hostalen 1770 PPT and having a melt index of 30 dg/minaccording to ASTM standard D 1238 at 230° C. under 5 kg, referred tohereinafter as B1, or a random propylene/ethylene copolymer containing14 mol % of units derived from ethylene, marketed under the nameVestolen P 2300 and having a melt index of 15 dg/min according to ASTMstandard D 1238, at 230° C. under 2.16 kg, referred to hereinafter asB2.

II. Conversion by injection.

1. Injection conditions.

All the compositions were prepared by compounding in a single-screwextruder under the same temperature conditions for a given startingpolymer. The blends were then converted into test specimens by injectioninto a mould at 20° C., according to a temperature profile of 210°C.-200° C.-190° C. and at an injection pressure of 950 bars.

2. Measurements carried out.

The following were measured on the test specimens obtained, ofstandardized dimensions:

the impact strength (IS) determined: either according to ISO standard R179 on notched test specimens, at -20° C. or -40° C., (referred tohereinafter as LS), expressed in kj/m², or according to French standardNFT 51118 (instrumented multiaxial impact, referred to hereinafter asIMI) on test specimens 1.7 mm in thickness, expressed by the force (F)at the point of failure, in newtons, and the energy (E) at the point offailure in joules at 23° C., or else

the elongation at break EB determined according to ASTM standard D 638,and expressed in %.

EXAMPLES 1 to 8 (COMPARATIVE)

Compounds made up of polymers to be modified and of the polymer (B) wereprepared according to the specifications in Table II below, which alsolists the results of the measurements which relate to them. The tensilestrength in the lengthwise direction LTS, determined according to ASTMstandard D 638, of a composition containing 80% by weight of polymer(P1) and 20% by weight of polymer (B1) is 155 daN/cm². The tensilestrength of a composition containing 80% by weight of polymer (P4) and20% by weight of polymer (B1) is 89 daN/cm² in the lengthwise direction(LTS) and 105 daN/cm² in the transverse direction (TTS).

EXAMPLES 9 TO 27

The compositions according to the invention were prepared by using, asfree radical inititator, a 2,2'-azobis(acetoxypropane) marketed underthe name Luazo AP (AP hereinafter) in the case of Examples 9 to 12 and22 to 27, or α,α'-bis(tert-butylperoxy)diisopropylbenzene marketed underthe name Perkadox Y 14/96 (Y hereinafter) in the case of Examples 14,16, 18, 20 and 21, and by following either of the operating methodsdescribed below.

a) First operating method (Examples 9 to 20):

Each of the polymers (A)n was prepared by adding to the correspondingpolymer to be modified (P)n a proportion (expressed in ppm and specifiedin Tables III and IV) of the initiator dispersed beforehand in aquantity of polymer (B) representing approximately 1 to 2% by weightrelative to the polymer (P) in a single-screw extruder with atemperature profile of 230°-290° C. (for the initiator AP) and with atemperature profile of 170°-220° C. (for the initiator Y) and for acontact time of 3 min. The ratio η_(o) ^(m) /η_(o) ^(c) of its measuredlimiting viscosity to its calculated limiting viscosity is shown inTables III and IV below.

The polymer (A) thus obtained was mixed with the polymer (B) in asingle-screw extruder at a temperature of 240° C. and for a period of 2min, in the proportion by weight shown in Tables III and IV. Theproperties of the compositions obtained are also shown in the sametables. Examples 13, 15, 17 and 19 are comparative (unmodifiedcopolymers P).

The tensile strength (LTS) values of compositions obtained according tothis first operating method, containing 80% by weight of polymer (A1)and 20% by weight of polymer (B1) are, respectively, 173 daN/cm² if thepolymer (A1) has been obtained by modifying the polymer (P1) with 200ppm of initiator AP, and 203 daN/cm² if the polymer (A1) has beenobtained by modifying the polymer (P1) with 375 ppm of the sameinitiator. Similarly, the tensile strength values of compositionscontaining 80% by weight of polymer (A4) and 20% by weight of polymer(B1) are, respectively: LTS=105 daN/cm² and TTS=125 daN/cm² if thepolymer (A4) had been obtained by modifying the polymer P4 with 450 ppmof initiator AP; they are LTS=103 daN/cm² and TTS=140 daN/cm² if thepolymer (A4) has been obtained with 850 ppm of the same initiator. Theelongation at break, in the lengthwise direction, of the composition ofExample 9 is 300%.

b) Second operating method (Examples 21 to 27)

A dispersion of the free radical initiator in a fraction of the polymer(B) was prepared in a first step by dry blending. This dispersion wasthen mixed with granules of polymer (B) and with granules of the polymerto be modified (P) in such quantities that the weight percentage of (B)in the final composition and that the proportion of initiator (expressedin ppm) relative to the polymer to be modified should be those specifiedin Table V. This granulate blend was extruded in a single-screw extruderwith a temperature profile of 230°-290° C. (for initiator AP) and with atemperature profile of 170°-220° C. (for initiator Y) and over a periodof 3 min. This produced the compositions which appear in Table V, wherethe results of the measurements carried out have also been shown.

III-Conversion into films by bubble blow-extrusion

1. Conditions of blow-extrusion

A Kiefel model 60 extruder fitted with an annular die permitting filmsof 50 μm thickness to be manufactured was employed. The blow ratio ofthe bubble (ratio of the bubble diameter to the die diameter) is 3. Thebubble is cooled with air at 20° C. at the die exit.

2. Measurements carried out

The maximum permissible output Q, up to which the blown bubble is stablewas determined for blow-extrusion. It is expressed in kg of compositionper hour.

The following were measured on the films obtained, 50 μm in thickness:

the impact strength Si, according to ASTM standard D 1709, expressed ingrams, and

the stiffness, expressed by means of the secant modulus at 1% elongationin the lengthwise direction (LSM) determined according to the NFstandard T 54102 and expressed in daN/cm².

EXAMPLES 28 TO 31

To begin with, compositions were prepared containing, on the one hand, acopolymer of ethylene and 1-butene marketed by CdF Chimie Ethylene etPlastiques under the name Lotrex FC 1010, containing 96 mol % of unitsderived from ethylene, having a melt index of 1 dg/min and a relativedensity of 0.918 and, on the other hand, the copolymer B2 alreadydescribed above.

The ethylene/1-butene copolymer present in these compositions wasmodified with 170 ppm of initiator AP, predispersed in a fraction of thepolymer B2 in a proportion of 2.5%, in a single-screw extruder at 190°C. The composition obtained was then granulated and the granulates wereconverted into films as indicated above.

Summarized in Table VI are the characteristics of the compositionsemployed (melt index (MI) according to ASTM standard D 1238 at 190° C.under 2.16 kg and relative density (d)) and the results obtained.

The results of Examples 30 and 31, given by way of comparison, wereobtained using ethylene/1-butene copolymers which had the same stiffnessas the compositions of Examples 28 and 29 according to the invention,respectively. It was found that, at equivalent stiffness, thecompositions according to the invention permit the extrusion rate to beincreased and the impact strength of the films obtained to be improved.

Unmodified compositions result in maximum outputs similar to those ofethylene/1-butene copolymers employed alone.

                  TABLE I                                                         ______________________________________                                        Polymer to                                                                    be modified                                                                           Trade name       % C.sub.2                                                                             d     MI                                     ______________________________________                                        P1      LOTREX MY 1610   99.8    0.960 16                                     P2      LOTREX MG 2200   98.2    0.940 20                                     P3      LOTREX MC 2300   96      0.920 20                                     P4      NORSOFLEX MW 1960                                                                              89.3    0.900 14                                     P5      NORSOFLEX FW 1900                                                                              88      0.900  1                                     P6      NORSOFLEX MW 2438                                                                              75.7    0.870  2                                     ______________________________________                                    

                  TABLE II                                                        ______________________________________                                              Nature of                                                                     the       % by weight                                                   Ex-   polymer   of polymer               EB                                   ample (P)       (B)        MI       IS   L    T                               ______________________________________                                        1     P3        20         14       4.8* 200  360                             2     P4        20         11       14**                                                                           10*                                      3     P4        40         8                                                                                      5**                                       4     P2        20         15            240  180                             5     P1        40         8.5            46   37                             6     P2        40         11             52   67                             7     P3        40         10             76   60                             8     P5        80         3.9      1.6* 265  828                             ______________________________________                                    

                  TABLE III                                                       ______________________________________                                                               .sub.η.sup.m.sub.o /.sub.η.sup.c.sub.o         Example                                                                              (A)     AP      (An)  % (B1)                                                                              MI        IS                               ______________________________________                                         9     A3      300      9    20    7.2       9*                               10     A4      450      8    20    6.9       31*                              11     A4      850     20    20    3.5       37**                                                                           33*                             12     A4      850     20    40    3.7                                                                                     29**                             ______________________________________                                         (*) at -20° C.                                                         (**) at -40° C.                                                   

                  TABLE IV                                                        ______________________________________                                               (A)                                                                           or                            IMI at 23° C.                     Example                                                                              (P)     Y       η.sub.o.sup.m /η.sub.o.sup.c                                                 % (B2) E     F                                  ______________________________________                                        13     P5      --      0.95   80     21.3  1210                               14     A5      200     80     80     26.7  1983                               15     P5      --      1      95     8.2   1470                               16     A5      100     50     95     11.2  2254                               17     P6      --      0.98   80     19.4  1150                               18     A6      750     95     80     27    1921                               19     P6      --      1      90     19.7  1350                               20     A6      250     75     90     23.2  2223                               ______________________________________                                    

                  TABLE V                                                         ______________________________________                                                               EB                                                     Example                                                                              (A)    AP      % (B1)                                                                              MI   IS    L     T                                ______________________________________                                        21     A5     200(Y)  80(B2)                                                                              3.3  3.1*  430                                    22     A3     450     20    7.1  10.5* 340   540                              23     A4     450     40    7.5  28*                                          24     A2     400     20    5.4        400   240                              25     A1     200     40    3           81    81                              26     A2     400     40    4          107   118                              27     A3     300     40    8          284   345                              ______________________________________                                         (*) at -20° C.                                                    

                  TABLE VI                                                        ______________________________________                                        Example % B2     MI      d     Q     Si    LSM                                ______________________________________                                        28      11       0.25    0.916 152   205   2130                               29      20       0.31    0.914 150    92   2650                               30       0       1       0.925 116   125   2100                               31       0       1       0.928 110    60   2600                               ______________________________________                                    

We claim:
 1. A non-crosslinked thermoplastic composition comprising:(a)less than 90% and at least 2% by weight of at least one polymer (A) of(i) ethylene or (ii) ethylene together with at least one α-olefincontaining from 3 to 12 carbon atoms, said polymer (A) comprising atleast 70 mol % of units derived from ethylene; and (b) more than 10% andup to 98% by weight of at least one polymer (B) containing at least 85mol % of units derived from at least one α-olefin containing from 3 to12 carbon atoms and not more than 15 mol % of units derived fromethylene; wherein said polymer (A) is a polymer modified by reactionwith at least one free radical initiator, the modified polymer having ameasured limiting viscosity between 1.3 and 100 times its limitingviscosity calculated from molecular mass distribution.
 2. A compositionaccording to claim 1, wherein said polymer (B) is an isotacticpolypropylene.
 3. A composition according to claim 1, wherein the meltindex of said polymer (B), at 230° C. under a load of 5 kg, is between0.2 and 150 dg/min.
 4. A composition according to claim 1, wherein saidpolymer (A) has a relative density of between 0.86 and 0.97.
 5. Acomposition according to claim 1, wherein the standard melt index ofsaid polymer (A) is between 0.05 and 150 dg/min.
 6. A compositionaccording to claim 5, wherein said standard melt index of said polymer(A) is between 10 and 30 dg/min.
 7. A composition according to claim 1,wherein, before being modified, said polymer (A) has been prepared bypolymerization by means of:(i) a Ziegler-type catalyst system comprisingat least one transition metal of groups IVA to VIA of the PeriodicClassification; or (ii) at least one activator comprising a Ziegler-typecatalyst as in (i) together with at least one organometallic derivativeof a metal of groups IA to IIIA of the Periodic Classification.